题目

The play had already been on for quite some time when we ____ at the New Theatre.   A. have arrived       B. arrived                C. had arrived             D. arrive   答案：B6．求不等式组$\left\{\begin{array}{l}{3（x-1）+2＜5x+3}\\{\frac{x-1}{2}+x≥3x-4}\end{array}\right.$的解集并把解集在数轴上表示出来，最后求出不等式组所有自然数解的和．